The present invention relates to an optical disk for recording, reproducing and erasing information. In particular, the present invention relates to an optical disk comprising write-once information that can be used for copyright protection, for example for copy-protection or protection from unauthorized use of software. Throughout this specification, xe2x80x9cwrite-once informationxe2x80x9d refers to information that is recorded after finishing the disk manufacturing process. The present invention relates further to a method for recording and a method for reproducing write-once information on the optical disk, an apparatus for reproducing the optical disk, an apparatus for recording and reproducing the optical disk, an apparatus for recording write-once information on the optical disk, and an apparatus for recording on the optical disk.
In recent years, the speed with which electronic calculators and information processing systems can process ever greater amounts of information has increased sharply. Together with the digitalization of audio and video information, this gave rise to the rapid dissemination of low-cost, high-volume auxiliary storage devices and recording media therefor, especially optical disks, which can be accessed with high access speeds.
The basic configuration of conventional optical disks is as follows: A dielectric layer is formed on top of a disk substrate, and a recording layer is formed on top of the dielectric layer. On top of the recording layer, an intermediate dielectric layer and a reflecting layer are formed in that order. An overcoat layer is formed on top of the reflecting layer.
The following is an explanation of how an optical disk with the above configuration is operated.
In the case of an optical disk having, in its recording layer, a magneto-optical layer with perpendicular magnetic anisotropy, the recording and erasing of information is performed by locally (a) heating the recording layer with a laser beam to a temperature with small coercive force above the compensation temperature or to a temperature near or above the Curie temperature to decrease the coercive force of the recording layer in the irradiated portion, and (b) magnetizing the recording layer in the direction of an external magnetic field. (This is also called xe2x80x9cthermomagnetic recordingxe2x80x9d of information.). Moreover, for the reproduction of the recording signal, a laser beam with less intensity than the laser beam for recording or erasing irradiates the recording layer. The recording state of the recording layer, that is, the rotation of the polarization plane of the light that is reflected or transmitted in accordance with the orientation of the magnetic field (this rotation occurs mainly due to two magneto-optical effectsxe2x80x94the Kerr effect and the Faraday effect), is detected by a photodetector through the change in the intensity of the irradiated light. In order to decrease the interference between opposite magnetizations and allow high-density recordings, a magnetic material with perpendicular magnetic anisotropy is used for the recording layer of the optical disk.
Moreover, when the data is reproduced, the reproduction signal level during data reproduction can be raised to detect the reproduction signal by using a layered structure for the recording layer: Several magnetic thin films comprising an exchange coupling multilayer or a magneto-static coupling multilayer.
For the recording layer, a material is used that can record information by locally raising the temperature or inducing a chemical reaction due to absorption of the irradiated laser light. The local variations in the recording layer can be detected by irradiating laser light of a different intensity or wavelength than that used for the recording and detecting the reproduction signal using the reflected or the transmitted light.
Regarding such optical disks, there is a need for a way to protect the data on the disk with write-once information (identification data) that allows for copyright protection, for example copy protection and protection against unauthorized use of software.
With the above configuration, it is possible to record disk information in TOC (or control data) areas, but when disk data is recorded with pre-pits, the disk information has to be administered stamper by stamper and cannot be administered user by user.
Moreover, when information is recorded using a magnetic film or a film of a phase-reversible material, administrative information easily can be changed, which means that it easily can be rewritten (manipulated), so that the contents on the optical disk cannot be copyright protected.
It is an object of the present invention to solve the problems of the prior art. It is a further object of the present invention to provide an optical disk comprising write-once information that can be used for copyright protection, for example for copy-protection or protection from unauthorized use of software, a method for recording write-once information on an optical disk, a method for reproducing write-once information from an optical disk, an apparatus for reproducing optical disks, an apparatus for recording and reproducing optical disks, an apparatus for recording write-once information on optical disks, and an apparatus for recording on optical disks.
In order to attain these objects, a first configuration of an optical disk in accordance with the present invention comprises a disk substrate and a recording layer on the disk substrate. The recording layer includes a magnetic film with a magnetic anisotropy in a direction perpendicular to a surface of the magnetic film. The optical disk stores write-once information formed by first recording areas and second recording areas in a pre-determined portion of the recording layer. A magnetic anisotropy in a direction perpendicular to a surface of the second recording areas is smaller than a magnetic anisotropy in a direction perpendicular to a surface of the first recording areas. The second recording areas are formed as strip-shaped marks that are oblong in a radial direction of the disk. A plurality of the marks is arranged in a circumferential direction of the disk, the arrangement being based on a modulation signal of the write-once information. In accordance with this first configuration, an optical disk can be achieved, which comprises write-once information that can be used for copyright protection, for example for copy-protection or protection from unauthorized use of software.
It is preferable that the optical disk according to the first configuration further comprises an identifier indicating whether there is a row of a plurality of marks arranged in a circumferential direction of the disk. With this configuration, the system can be started in a short time. Moreover, in this configuration, it is preferable that the identifier indicating the row of marks is stored among control data. With this configuration, it is known when the control data is reproduced whether write-once information is stored, so that the write-once information can be reproduced reliably.
It is preferable that in the optical disk according to the first configuration, the pre-determined portion comprising write-once information is at an inner perimeter portion of the disk. With this configuration, the position of the optical head with respect to a radial direction of the disk can be determined with an optical head stopper or address information of a bit signal.
It is preferable that in the optical disk according to the first configuration, a difference between a luminous energy that is reflected from the first recording areas and a luminous energy that is reflected from the second recording areas is below a certain value. It is particularly preferable that the difference between luminous energy that is reflected from the first recording areas and luminous energy that is reflected from the second recording areas is not more than 10%. With this configuration, variations of the reproduction waveform accompanying changes of the reflected luminous energy can be suppressed.
It is preferable that in the optical disk according to the first configuration, a difference between an average refractive index of the first recording areas and an average refractive index of the second recording areas is not more than 5%. With this configuration, the difference between luminous energy that is reflected from the first recording areas and luminous energy that is reflected from the second recording areas can be adjusted to not more than 10%.
It is preferable that in the optical disk according to the first configuration, the magnetic anisotropy of the magnetic film of the second recording areas in an in-plane direction is dominant. With this configurations using a reading device having a polarizer and a photo-detector the reproduction signal of the first recording areas, which corresponds to the write-once information, can be attained. Thus, the write-once information can be obtained rapidly and without using an optical head.
It is preferable that in the optical disk according to the first configuration, at least a portion of the magnetic film of the second recording areas is crystallized. With this configuration, the magnetic anisotropy perpendicular to the magnetic film of the second recording areas can be almost completely eliminated, so that the reproduction signal can be reliably detected as the difference of the polarization orientation to the first recording areas.
It is preferable that in the optical disk according to the first configuration, the recording layer comprises a multilayer magnetic film. With this configuration, the magnetically induced super resolution method xe2x80x9cFADxe2x80x9d can be used as the reproduction method. Thus, signal reproduction with regions smaller than the laser beam spot becomes possible.
A second configuration of an optical disk in accordance with the present invention comprises a disk substrate and a recording layer on the disk substrate. The recording layer includes a film that can be reversibly changed between two optically detectable states. The optical disk stores write-once information formed by first recording areas and second recording areas in a predetermined portion of the recording layer. A luminous energy that is reflected from the first recording areas differs from a luminous energy that is reflected from the second recording areas. The second recording areas are formed as stripe-shaped marks that are oblong in a radial direction of the disk. A plurality of the marks is arranged in a circumferential direction of the disk, the arrangement being based on a modulation signal for the write-once information. In accordance with this second configuration, an optical disk can be achieved, which comprises write-once information that can be used for copyright protection, for example for copy-protection or protection from unauthorized use of software.
It is preferable that the optical disk according to the first configuration further comprises an identifier for indicating whether there is a row of a plurality of marks arranged in a circumferential direction of the disk. Moreover, it is preferable that the identifier indicating the row of marks is stored among control data.
It is preferable that in the optical disk according to the first configuration, the pre-determined portion comprising write-once information is at an inner perimeter portion of the disk.
It is preferable that in the optical disk according to the first configuration, the recording layer undergoes a reversible phase change between a crystalline phase and an amorphous phase, depending on irradiation conditions for irradiated light. With this configuration, information can be recorded by utilizing an optical difference based on a reversible structural change at the atomic level. Moreover, information can be reproduced as a difference of the reflected luminous energy or the transmitted luminous energy at a certain wavelength. Moreover, in this case, it is preferable that the difference between luminous energy that is reflected from the first recording areas and luminous energy that is reflected from the second recording areas is at least 10%. With this configuration, a reproduction signal of the first recording area, which corresponds to the write-once information, can be obtained reliably. Moreover, in this case, it is preferable that a difference between an average refractive index of the first recording areas and an average refractive index of the second recording areas is at least 5%. With this configuration, the difference between the luminous energy reflected from the first recording areas and the luminous energy reflected from the second recording areas can be adjusted to at least 10%. Moreover, in this case, it is preferable that the second recording areas of the recording layer are in a crystalline phase. With this configuration, recording can be performed with excessive laser power. Furthermore, since the luminous energy reflected from the crystalline phase can be large, detection of the reproduction signal becomes easy. Moreover, in this case, it is preferable that the recording layer comprises a Gexe2x80x94Sbxe2x80x94Te alloy.
In a third configuration of an optical disk in accordance with the present invention, main information and write-once information is recorded, the write-once information being different for each disk, and the write-once information storing at least watermark production parameters for producing a watermark. In accordance with this third configuration, the following operations can be performed: When the watermark production parameters and the disk ID are recorded in the write-once information with absolutely no correlation between the disk ID and the watermark production parameters, it becomes impossible to guess the watermark from the disk ID. Thus, an illegal copier issuing a new ID and issuing an improper watermark can be prevented.
It is preferable that in the optical disk according to the third configuration, the main information is recorded by providing convex-concave pits in a reflective layer, and the write-once information is recorded by partially removing the reflective layer.
It is preferable that in the optical disk according to the third configuration, the main information and the write-once information are recorded by partially changing a reflection coefficient of a reflective layer.
It is preferable that in the optical disk according to the third configuration, a recording layer comprises a magnetic layer with a magnetic anisotropy in a direction perpendicular to a surface of the magnetic layer, the main information is recorded by partially changing a magnetization direction of the recording layer, and the write-once information is recorded by partially changing the magnetic anisotropy in the direction perpendicular to the surface of the magnetic layer.
A first method for recording write-once information onto an optical disk (a) comprising a disk substrate, and a recording layer on the disk substrate, including a magnetic film with a magnetic anisotropy in a direction perpendicular to a surface of the magnetic film; and (b) storing write-once information formed by first recording areas and second recording areas in a pre-determined portion of the recording layer; comprises forming the second recording areas as a plurality of stripe-shaped marks that are oblong in a radial direction of the disk in a circumferential direction of the disk by irradiating laser light based on a modulation signal of the write-once information in a circumferential disk direction in the pre-determined portion of the recording layer in a manner that a magnetic anisotropy in a direction perpendicular to a surface of the second recording areas becomes smaller than a magnetic anisotropy in a direction perpendicular to a surface of the first recording areas. In accordance with this first method for recording write-once information onto an optical disk, write-once information that can be used for copyright protection, for example for copy-protection or protection from unauthorized use of software, can be efficiently recorded onto an optical disk.
It is preferable that in the first method for recording write-once information, when the second recording areas are formed, a laser light source is pulsed in accordance with a modulation signal of phase-encoded write-once information, and the optical disk or the laser light is rotated. With this configuration, rotation variations can be eliminated, especially when the clock of a rotation sensor is used, so that the write-once information can be recorded with little fluctuations of the channel clock period.
It is preferable that in the first method for recording write-once information, the optical disk further comprises a reflective layer and a protective layer on the disk substrate, and an intensity of laser light irradiated to form the second recording areas is smaller than an intensity of laser light destroying at least one of the disk substrate, the reflective layer and the protective layer. With this configuration, write-once information can be recorded at software companies or retailers.
It is preferable that in the first method for recording write-once information, an intensity of laser light irradiated to form the second recording areas is an intensity for crystallizing at least a portion of the recording layer. With this configuration, the magnetic anisotropy of the recording layer perpendicular to the surface of the recording layer cannot be restored, so that manipulation of the write-once information can be prevented.
It is preferable that in the first method for recording write-once information, an intensity of laser light irradiated to form the second recording areas is larger than an intensity of laser light heating the recording layer to a Curie temperature. With this configuration, it is possible to decrease or eliminate the magnetic anisotropy of the recording layer perpendicular to the surface of the recording layer, especially when the intensity of the laser light is excessive.
It is preferable that in the first method for recording write-once information, an intensity of laser light irradiated to form the second recording areas is an intensity for making a magnetic anisotropy of the magnetic layer of the first recording areas in an in-plane direction dominant.
It is also preferable that in the first method for recording write-once information, rectangularly stripe-shaped laser light is irradiated with a unidirectional convergence focusing lens onto the recording layer when the second recording areas are formed.
It is also preferable that in the first method for recording write-once information, a light source of the laser light that is irradiated for forming the second recording areas is a YAG laser. In this case, it is preferable that a magnetic field above a certain value is applied to the recording layer while irradiating laser light from the YAG laser. With this configuration, write-once information can be recorded easily by partially changing the magnetic anisotropy perpendicular to the surface of the recording layer after aligning the magnetic anisotropy in a direction perpendicular to the surface of the recording layer. In this case, it is even more preferable that the magnetic field applied to the recording layer is at least 5 kOe.
A second method for recording write-once information onto an optical disk (a) comprising a disk substrate; and on the disk substrate a recording layer comprising a film that can be reversibly changed between two optically detectable states; and (b) storing write-once information formed by first recording areas and second recording areas in a pre-determined portion of the recording layer; comprises forming the second recording areas as a plurality of stripe-shaped marks that are oblong in a radial direction of the disk in a circumferential direction of the disk by irradiating laser light based on a modulation signal of the write-once information in a circumferential disk direction in the pre-determined portion of the recording layer in a manner that a luminous energy of light reflected from the first recording areas differs from a luminous energy of light reflected from the second recording areas. In accordance with this second method for recording write-once information onto an optical disk, write-once information that can be used for copyright protection, for example for copy-protection or protection from unauthorized use of software, can be efficiently recorded onto an optical disk.
It is preferable that in the second method for recording write-once information, when the second recording areas are formed, a laser light source is pulsed in accordance with a modulation signal of phase-encoded write-once information, and the optical disk or the laser light is rotated.
It is also preferable that in the second method for recording write-once information, the optical disk further comprises a reflective layer and a protective layer on the disk substrate, and an intensity of laser light irradiated to form the second recording areas is smaller than an intensity of laser light destroying at least one of the disk substrate, the reflective layer and the protective layer.
It is also preferable that in the second method for recording write-once information, an intensity of laser light irradiated to form the second recording areas is an intensity for crystallizing at least a portion of the recording layer.
It is also preferable that in the second method for recording write-once information, rectangularly stripe-shaped laser light is irradiated onto the recording layer with a unidirectional convergence focusing lens when the second recording areas are formed. In this case, it is also preferable that a light source of the laser light that is irradiated for forming the second recording areas is a YAG laser.
A third method for recording write-once information onto an optical disk comprises producing a watermark based on a disk ID; and overlapping the watermark on specific data to record it as write-once information. In accordance with this third method for recording write-once information onto an optical disk, the disk ID can be detected from the watermark, so that the origin of illegal copies can be determined.
A first method for reproducing write-once information from an optical disk (a) comprising a disk substrate, and a recording layer on the disk substrate, the recording layer including a magnetic film with a magnetic anisotropy in a direction perpendicular to a surface of the magnetic film; and (b) storing write-once information formed by first recording areas and second recording areas in a pre-determined portion of the recording layer, the first and second recording layers having different magnetic anisotropies in a direction perpendicular to a surface of the magnetic layer; comprises irradiating linearly polarized laser light onto the pre-determined portion; and detecting a change in a polarization orientation of light reflected from the optical disk or light transmitted through the optical disk. In accordance with this first method for reproducing write-once information from an optical disk, the write-once information can be reproduced easily.
It is preferable that in the first method for reproducing write-once information, the linearly polarized laser light is irradiated onto the pre-determined portion after magnetizing the recording layer of the pre-determined portion in one step by applying a magnetic field that is larger than a coercive force of the recording layer in the pre-determined portion. With this configuration, the polarization orientation detected from the first recording areas is normally constant, and the reproduction signal can be obtained with a stable amplitude from the difference with respect to the polarization orientation of the second recording areas.
It is also preferable that in the first method for reproducing write-once information, the linearly polarized laser light is irradiated onto the pre-determined portion after aligning a magnetization of the recording layer of the pre-determined portion by applying a unidirectional magnetic field to the predetermined portion while increasing the temperature of the recording layer in the pre-determined portion above the Curie temperature by irradiating laser light of constant luminous energy. With this configuration, after recording the write-once information, the signal can be reliably reproduced without being influenced by outside magnetic fields or the like.
A second method for reproducing write-once information from an optical disk (a) comprising a disk substrate; and a recording layer on the disk substrate, the recording layer including a film that can be reversibly changed between two optically detectable states; and (b) storing write-once information formed by first recording areas and second recording areas with different reflection coefficients in a pre-determined portion of the recording layer; comprises irradiating focused laser light onto the pre-determined portion; and detecting a change in a luminous energy reflected from the disk. In accordance with this second method for reproducing write-once information from an optical disk, the write-once information can be reproduced easily.
A first configuration of an apparatus for reproducing optical disks comprising (a) a main information recording area for recording main information; and (b) an auxiliary signal recording area overlapping partly with the main information recording area for recording a phase-encoding modulated auxiliary signal that overlaps a signal of main information, comprises means for reproducing a main information signal in the main information recording area with an optical head; first decoding means for decoding a main information signal to obtain main information data; means for reproducing a mixed signal comprising a main information signal in the auxiliary signal recording area and the auxiliary signal as a reproduction signal with the optical head; frequency separation means for suppressing the main information signal in the reproduction signal to obtain the auxiliary signal; and second decoding means for phase-encoding decoding the auxiliary signal to obtain the auxiliary data. In accordance with this first configuration of an apparatus for reproducing optical disks, the decoding data of the auxiliary signal can be reproduced reliably.
It is preferable that in the apparatus for reproducing optical disks according to the first configuration, the frequency separation means is a low-frequency component separation means for suppressing high frequency components in the reproduction signal reproduced with the optical head to obtain a low frequency reproduction signal, and that the apparatus further comprises a second-slice-level setting portion for producing a second slice level from the low-frequency reproduction signal; and a second-level slicer for slicing the low-frequency reproduction signal at the second slice level to obtain a binarized signal; wherein the apparatus phase-encoding decodes the binarized signal to obtain the auxiliary data. With this configuration, errors due to variations of the envelope of the reproduction signal of the write-once information can be prevented. In this case, it is preferable that the second-slice-level setting portion comprises auxiliary low-frequency component separation means with a time constant that is larger than that of the low-frequency component separation means; a reproduction signal reproduced with the optical head or a low-frequency reproduction signal obtained with the low-frequency component separation means is entered into the auxiliary low-frequency component separation means; and components with frequencies lower than the low-frequency reproduction signal are extracted to obtain a second slice level. With this configuration, the slice level can be set following the level variations of low frequency components, so that the signal easily can be reproduced.
It is preferable that the apparatus for reproducing optical disks according to the first configuration further comprises frequency transformation means for transforming a main information signal included in a reproduction signal reproduced with the optical head from a time domain into a frequency domain to produce a first transformation signal; means for producing a mixed signal, wherein auxiliary information has been added or superposed to the first transformation signal; and frequency inverse-transformation means for transforming the mixed signal from the frequency domain to the time domain to produce a second transformation signal. With this configuration, the ID signal can be spectrally dispersed, so a deterioration of the video signal, which corresponds to the main information, can be prevented, and the reproduction of the main information becomes easier.
In a second configuration of an apparatus for reproducing optical disks, an optical head irradiates linearly polarized light onto an optical disk, and a change of a polarization orientation of light that is transmitted or reflected from the optical disk is detected in accordance with a recording signal on the optical disk. The apparatus comprises means for moving, when necessary, the optical head into a pre-determined portion of the optical disk where write-once information is stored, and means for reproducing the write-once information after detecting a change of a polarization orientation of light that is transmitted or reflected from the pre-determined portion. In accordance with this second configuration of an apparatus for reproducing optical disks, the reproduction signal can be detected easily, because it is not influenced by variations of the reflected luminous energy or by noise components included in the addition signal.
It is preferable that the apparatus for reproducing optical disks according to the second configuration further comprises means for detecting an identifier indicating whether write-once information within control data of the optical disk is present, the indication being based on a detection signal of detection light that is received with at least one photo-detector of the optical head or on an addition signal of detection signals of detection light that is received with a plurality of photo-detectors of the optical head, wherein to detect the identifier and to verify whether write-once information is present, the optical head is moved to the pre-determined portion of the optical disk where write-once information is stored, when necessary. With this configuration, stripes and defects in the write-once information easily can be discriminated, so that the start-up time for the apparatus can be considerably shortened.
It is preferable that the apparatus for reproducing optical disks according to the second configuration further comprises decoding means for phase-encoding decoding during reproduction of the write-once information. This configuration can be used for the reproduction of write-once information, such as an ID signal.
In a third configuration of an apparatus for reproducing optical disks whereon main information is stored and write-once information that differs for each disk is stored, the apparatus comprises a signal reproduction portion for reproducing the main information; a write-once information reproduction portion for reproducing the write-once information; and a watermark attaching portion for producing a watermark signal based on the write-once information, adding the watermark signal to the main information and giving it out. In accordance with this third configuration of an apparatus for reproducing optical disks, illegal copies being made to obtain the main information of, for example, the video signal can be prevented.
It is preferable that in the apparatus for reproducing optical disks according to the third configuration, the write-once information is recorded by partially changing a reflection coefficient of a recording layer on the optical disk.
It is also preferable that in the apparatus for reproducing optical disks according to the third configuration, a recording layer of the optical disk comprises a magnetic film having a magnetic anisotropy that is perpendicular to a film surface; and write-once information is stored by partially changing the perpendicular magnetic anisotropy of the magnetic film.
It is also preferable that in the apparatus for reproducing optical disks according to the third configuration, a watermark attaching portion overlaps a signal of the main information with auxiliary information comprising a watermark. With this configuration, the auxiliary information being deleted from the main information with a normal recording and reproducing system can be prevented.
It is also preferable that the apparatus for reproducing optical disks according to the third configuration further comprises a frequency transformation means for producing a first transformation signal by transforming a signal of main information from a time domain into a frequency domain; means for producing a mixed signal by adding or superposing write-once information and the first transformation signal; and frequency inverse-transformation means for producing a second transformation signal by transforming the mixed signal from the frequency domain into the time domain.
It is also preferable that the apparatus for reproducing optical disks according to the third configuration further comprises an MPEG decoder for expanding main information into a video signal; and means for inputting the video signal into the watermark attaching portion. With this configuration, the watermark can be spectrally dispersed and added to the main information, such as the video signal, without deteriorating the signal. In this case, it is preferable that the apparatus further comprises a watermark reproduction portion for reproducing watermarks; the MPEG decoder and the watermark reproduction portion both comprise a mutual authentication portion; and encrypted main information is sent and decrypted only if the mutual authentication portions authenticate each other. With. this configuration, illegal elimination or manipulation of watermarks can be prevented, because the encryption is not cancelled when the digital signal is intercepted from an intermediate bus. In this case, it is preferable that a compound signal of main information that is compounded with an encryption decoder is input into the MPEG decoder. With this configuration, there is no correlation between information such as the ID and the watermark production parameters, so that illegal copies with unauthorized watermarks can be prevented. In this case, it is even more preferable that the apparatus further comprises a watermark reproduction portion for reproducing watermarks; an encryption decoder and the watermark reproduction portion both comprise a mutual authentication portion; and encrypted main information is sent and decrypted only if the mutual authentication portions authenticate each other.
In a first configuration of an apparatus for recording and reproducing optical disks whereon information can be recorded, erased and reproduced and whereon main information is stored on a main recording area of a recording layer of the optical disks using a recording circuit and an optical head, the apparatus comprises means for reproducing write-once information that is recorded onto a pre-determined portion of the recording layer using a signal output portion of the optical head, which detects the write-once information as a change of a polarization orientation; means for recording the main information onto the main recording area as encrypted information that is encrypted with an encryption encoder using the write-once information; and means for reproducing the main information by reproducing the write-once information with the signal output portion of the optical head and composing the encrypted information as a decryption key in an encryption decoder. In accordance with this first configuration of an apparatus for recording and reproducing optical disks, illegal copies can be prevented, so that the copyright can be protected.
In a second configuration of an apparatus for recording and reproducing optical disks whereon main information is recorded onto a main recording area of a recording layer of the optical disks using a recording circuit and an optical head, the apparatus comprises a watermark attaching portion for adding a watermark to the main information. Write-once information that is stored in a pre-determined portion of the recording layer is reproduced with the optical head. The reproduced write-once information is added to the main information as a watermark with the watermark attaching portion. The main information including the watermark is recorded onto the main recording area. In accordance with this second configuration of an apparatus for recording and reproducing optical disks, the recording history can be traced from the watermark recording data, so that illegal copies and illegal use can be prevented.
It is preferable that in the apparatus for recording and reproducing optical disks according to the second configuration, the main information is recorded by partially changing a reflection coefficient of the recording layer.
It is also preferable that in the apparatus for recording and reproducing optical disks according to the second configuration, the recording layer comprises a magnetic film having a magnetic anisotropy that is perpendicular to a film surface; and main information is stored by partially changing a magnetization direction of the magnetic film. In this case, it is preferable that the main information and the write-once information are reproduced by detecting a change of a magnetization orientation of the recording layer or a change of the perpendicular anisotropy of the recording layer with an optical head as a change of a polarization orientation.
It is also preferable that in the apparatus for recording and reproducing optical disks according to the second configuration, a watermark attaching portion overlaps a signal of the main information with auxiliary information comprising a watermark.
It is also preferable that the apparatus for recording and reproducing optical disks according to the second configuration further comprises a frequency transformation means for producing a first transformation signal by transforming a signal of main information from a time domain into a frequency domain; means for producing a mixed signal by adding or superposing write-once information and the first transformation signal; and frequency inverse-transformation means for producing a second transformation signal by transforming the mixed signal from the frequency domain into the time domain.
It is also preferable that the apparatus for recording and reproducing optical disks according to the second configuration further comprises an MPEG decoder for expanding main information into a video signal; and means for inputting the video signal into the watermark attaching portion. In this case, it is preferable that the apparatus further comprises a watermark reproduction portion for reproducing watermarks; the MPEG decoder and the watermark reproduction portion both comprise a mutual authentication portion; and encrypted main information is sent and decrypted only if the mutual authentication portions authenticate each other. It is also preferable that a compound signal of main information that is compounded with an encryption decoder is input into the MPEG decoder. It is even more preferable that the apparatus further comprises a watermark reproduction portion for reproducing watermarks; the encryption decoder and the watermark reproduction portion both comprise a mutual authentication portion; and encrypted main information is sent and decrypted only if the mutual authentication portions authenticate each other.
In a configuration of an apparatus for recording write-once information onto an optical disk storing main information, the apparatus comprises means for recording auxiliary information comprising at least one of a disk ID and watermark production parameters. In accordance with this configuration of an apparatus for recording write-once information onto an optical disk, it can be determined from the disk ID or the watermark who made an illegal copy or illegal use of the disk, so that the copyright can be protected.
It is preferable that in the apparatus for recording write-once information onto an optical disk according to this configuration, the main information is stored by providing convex/concave pits in a reflection film of the optical disk, and the auxiliary information is stored by partially erasing the reflection film.
It is also preferable that in the apparatus for recording write-once information onto an optical disk according to this configuration, the main information is stored by partially changing a reflection coefficient of a recording layer of the optical disk, and the auxiliary information is stored by partially changing a reflection coefficient of the recording layer of the optical disk.
It is also preferable that in the apparatus for recording write-once information onto an optical disk according to this configuration, a recording layer of the optical disk comprises a magnetic film having a magnetic anisotropy that is perpendicular to a film surface; main information is stored by partially changing a magnetization direction of the magnetic film; and auxiliary information is stored by partially changing the perpendicular magnetic anisotropy of the magnetic film.
In a configuration of an apparatus for recording optical disks storing main information, the apparatus comprises means for producing a watermark based on auxiliary information comprising a disk ID; and means for recording data, which consists of certain data to which the watermark has been superposed. In accordance with this configuration of an apparatus for recording optical disks storing main information, the watermark can be detected from the recorded data, and the contents history can be determined, so that the copyright can be protected.